Nominally forbidden transitions in the interband optical spectrum of quantum dots

We calculate the excitonic optical absorption spectra of (In,Ga)As/GaAs self-assembled quantum dots by adopting an atomistic pseudopotential approach to the single-particle problem followed by a configuration-interaction approach to the many-body problem. We find three types of allowed transitions that would be naively expected to be forbidden. (i) Transitions that are parity forbidden in simple effective mass models with infinite confining wells (e.g. 1S-2S, 1P-2P) but are possible by finite band-offsets and orbital-mixing effects; (ii) light-hole--to--conduction transitions, enabled by the confinement of light-hole states; and (iii) transitions that show and enhanced intensity due to electron-hole configuration mixing with allowed transitions. We compare these predictions with results of 8-band k.p calculations as well as recent spectroscopic data. Transitions in (i) and (ii) explain recently observed satellites of the allowed P-P transitions.Comment: Version published in Phys. Rev.

Factorization and Scaling in Hadronic Diffraction

In standard Regge theory with a pomeron intercept a(0)=1+\epsilon, the contribution of the tripe-pomeron amplitude to the t=0 differential cross section for single diffraction dissociation has the form d\sigma/dM^2(t=0) \sim s^{2\epsilon}/(M^2)^{1+\epsilon}. For \epsilon>0, this form, which is based on factorization, does not scale with energy. From an analysis of p-p and p-pbar data from fixed target to collider energies, we find that such scaling actually holds, signaling a breakdown of factorization. Phenomenologically, this result can be obtained from a scaling law in diffraction, which is embedded in the hypothesis of pomeron flux renormalization introduced to unitarize the triple pomeron amplitude.Comment: 39 pages, Latex, 16 figure

Survey of charge symmetry breaking operators for dd -> alpha pi0

The charge-symmetry-breaking amplitudes for the recently observed d d -> alpha pi0 reaction are investigated. Chiral perturbation theory is used to classify and identify the leading-order terms. Specific forms of the related one- and two-body tree level diagrams are derived. As a first step toward a full calculation, a few tree-level two-body diagrams are evaluated at each considered order, using a simplified set of d and alpha wave functions and a plane-wave approximation for the initial dd state. The leading-order pion-exchange term is shown to be suppressed in this model because of poor overlap of the initial and final states. The higher-order one-body and short-range (heavy-meson-exchange) amplitudes provide better matching between the initial and final states and therefore contribute significantly and coherently to the cross section. The consequences this might have for a full calculation, with realistic wave functions and a more complete set of amplitudes, are discussed.Comment: REVTeX 4, 35 pages, 8 eps figures, submitted to PR

Influence of chronic nitrate intoxication on the concentration of lipid hydroperoxides in the gastric mucosa

The excessive alimentary intake of nitrates into human and animal body can cause a cascade of changes in their organism. The sources of nitrates can be either products of vegetable origin (especially beetroot) or groundwater and drinking water (regions with developed agriculture). The first system of organs, which experiences the negative effect of nitrates, is the digestive system. The purpose of this work was to establish the effect of chronic nitrate intoxication on the content of lipid hydroperoxides in rat stomach mucous membrane. Materials and methods. We carried out experiment on 24 white rats. We divided animals into 2 groups: the control group (10) and the group of chronic nitrate intoxication (14). We modeled chronic nitrate intoxication by intragastric administration of sodium nitrate at a dose of 500 mg / kg for 30 days. The content of lipid hydroperoxides in 10% of the mucous membrane homogenate was determined by the method of VB Gavrilov. and MI Mishkorudnaya (1983). We analyzed the obtained results for normality by the Shapiro-Wilk method. Further, we compared data by the Student method. The difference was considered statistically significant if p <0.05. Results and discussion. Chronic nitrate intoxication reduces the content of dien conjugates (DC) in the gastric mucosa by 8% relative to the control group. The concentration of triene conjugates (TC) increases by 20.51%. The content of octadiene conjugates (ODC) increases by 52.2%. Decrease in the concentration of DC under conditions of nitrate intoxication, we can explain by the increase in activity of superoxide dismutase [1]. The remaining hydroperoxides are products of the later stages of lipid peroxidation (LPO), which is controlled by the glutathione system. Thus, it can be argued that the excessive intake of nitrates in the body leads to a disruption in the functioning of the glutathione system. Conclusion. Excess intake of nitrates in the body prevents the activation of LPO on early stages, but enhances lipid oxidation that has already begun

GEM operation in helium and neon at low temperatures

We study the performance of Gas Electron Multipliers (GEMs) in gaseous He, Ne and Ne+H2 at temperatures in the range of 2.6-293 K. In He, at temperatures between 62 and 293 K, the triple-GEM structures often operate at rather high gains, exceeding 1000. There is an indication that this high gain is achieved by Penning effect in the gas impurities released by outgassing. At lower temperatures the gain-voltage characteristics are significantly modified probably due to the freeze-out of impurities. In particular, the double-GEM and single-GEM structures can operate down to 2.6 K at gains reaching only several tens at a gas density of about 0.5 g/l; at higher densities the maximum gain drops further. In Ne, the maximum gain also drops at cryogenic temperatures. The gain drop in Ne at low temperatures can be reestablished in Penning mixtures of Ne+H2: very high gains, exceeding 10000, have been obtained in these mixtures at 50-60 K, at a density of 9.2 g/l corresponding to that of saturated Ne vapor near 27 K. The results obtained are relevant in the fields of two-phase He and Ne detectors for solar neutrino detection and electron avalanching at low temperatures.Comment: 13 pages, 14 figures. Accepted for publishing in Nucl. Instr. and Meth.

Excitonic photoluminescence in symmetric coupled double quantum wells subject to an external electric field

The effect of an external electric field F on the excitonic photoluminescence (PL) spectra of a symmetric coupled double quantum well (DQW) is investigated both theoretically and experimentally. We show that the variational method in a two-particle electron-hole wave function approximation gives a good agreement with measurements of PL on a narrow DQW in a wide interval of F including flat-band regime. The experimental data are presented for an MBE-grown DQW consisting of two 5 nm wide GaAs wells, separated by a 4 monolayers (MLs) wide pure AlAs central barrier, and sandwiched between Ga_{0.7}Al_{0.3}As layers. The bias voltage is applied along the growth direction. Spatially direct and indirect excitonic transitions are identified, and the radius of the exciton and squeezing of the exciton in the growth direction are evaluated variationally. The excitonic binding energies, recombination energies, oscillator strengths, and relative intensities of the transitions as functions of the applied field are calculated. Our analysis demonstrates that this simple model is applicable in case of narrow DQWs not just for a qualitative description of the PL peak positions but also for the estimation of their individual shapes and intensities.Comment: 5 pages, 4 figures (accepted in Phys. Rev. B

Improved detection of differentially represented DNA barcodes for high-throughput clonal phenomics

Cellular DNA barcoding has become a popular approach to study heterogeneity of cell populations and to identify clones with differential response to cellular stimuli. However, there is a lack of reliable methods for statistical inference of differentially responding clones. Here, we used mixtures of DNA-barcoded cell pools to generate a realistic benchmark read count dataset for modelling a range of outcomes of clone-tracing experiments. By accounting for the statistical properties intrinsic to the DNA barcode read count data, we implemented an improved algorithm that results in a significantly lower false-positive rate, compared to current RNA-seq data analysis algorithms, especially when detecting differentially responding clones in experiments with strong selection pressure. Building on the reliable statistical methodology, we illustrate how multidimensional phenotypic profiling enables one to deconvolute phenotypically distinct clonal subpopulations within a cancer cell line. The mixture control dataset and our analysis results provide a foundation for benchmarking and improving algorithms for clone-tracing experiments

Blue laser cooling transitions in Tm I

We have studied possible candidates for laser cooling transitions in $^{169}$Tm in the spectral region 410 -- 420 nm. By means of saturation absorption spectroscopy we have measured the hyperfine structure and rates of two nearly closed cycling transitions from the ground state $4\textrm{f}^{13}6\textrm{s}^2(^2\textrm{F}_0)(J_g=7/2)$ to upper states $4\textrm{f}^{12}(^3\textrm{H}_5)5\textrm{d}_{3/2}6\textrm{s}^2(J_e=9/2)$ at 410.6 nm and $4\textrm{f}^{12}(^3\textrm{F}_4)5\textrm{d}_{5/2}6\textrm{s}^2(J_e=9/2)$ at 420.4 nm and evaluated the life times of the excited levels as 15.9(8) ns and 48(6) ns respectively. Decay rates from these levels to neighboring opposite-parity levels are evaluated by means of Hartree-Fock calculations. We conclude, that the strong transition at 410.6 nm has an optical leak rate of less then $2\cdot10^{-5}$ and can be used for efficient laser cooling of $^{169}$Tm from a thermal atomic beam. The hyperfine structure of two other even-parity levels which can be excited from the ground state at 409.5 nm and 418.9 nm is also measured by the same technique. In addition we give a calculated value of $7(2)$ s$^{-1}$ for the rate of magnetic-dipole transition at 1.14 $\mu$m between the fine structure levels $(J_g=7/2)\leftrightarrow(J'_g=5/2)$ of the ground state which can be considered as a candidate for applications in atomic clocks.Comment: 8 pages, 5 figure

Room temperature plasmon laser by total internal reflection

Plasmon lasers create and sustain intense and coherent optical fields below light's diffraction limit with the unique ability to drastically enhance light-matter interactions bringing fundamentally new capabilities to bio-sensing, data storage, photolithography and optical communications. However, these important applications require room temperature operation, which remains a major hurdle. Here, we report a room temperature semiconductor plasmon laser with both strong cavity feedback and optical confinement to 1/20th of the wavelength. The strong feedback arises from total internal reflection of surface plasmons, while the confinement enhances the spontaneous emission rate by up to 20 times.Comment: 8 Page, 2 Figure